Mercury delay line from the ACE computer, NPL

Mercury delay line memory unit from the ACE computer, National Physical Laboratory (NPL), 1958-1967, based on Alan Turing's design

Designed by Alan Turing in 1946, the Automatic Computing Engine (ACE) was the first complete specification of an electronic stored program all purpose digital computer. It was built at the National Physical Laboratory and contained 200 delay lines, 7000 valves and 48 bit word size. The ACE was designed to fully exploit the potential of a mercury delay line memory. Delay lines were developed for radar during the Second World War, then adapted to be used in early computers. Programs were fed into the machine using punched paper tape, which generated pulses that the computer used to store the program and perform the desired calculation.

By the time ACE was completed in 1958, the hey day of delay line storage was over, and contemporary computers were using random access storage and transistors. While no longer a machine of its time, Turing’s vision for the ACE had a significant impact on British and American computing industries, spinning off several derivatives including the NPL Pilot ACE, English Electric DEUCE, MOSAIC and Bendix G 15. This short delay line, donated by the family of NPL engineer Dr David Yates, is a rare artefact from the ACE and symbolic of Turing’s influential work on modern computing science. Dr David Yates worked at NPL from 1962 to 1992, during which time he managed ‘Scrapbook’, an information storage and retrieval system that went live in mid-1971. It included what would now be called word processing, e-mail and hypertext. He wrote ‘Turing’s Legacy: A History of Computing at The National Physical Laboratory, 1945-1995’, published by the Science Museum in 1997.